The present invention is directed to implantable devices for stabilizing the spine. Specifically, the invention concerns intervertebral spacers expandable from a reduced size insertion configuration to an expanded size spacing configuration.
Intervertebral discs, located between the end plates of adjacent vertebrae, stabilize the spine, distribute forces between vertebrae and cushion vertebral bodies. An intervertebral disc may deteriorate due to trauma, aging or disease resulting in pain or discomfort to a patient. One common procedure for relief of patient discomfort is a discectomy, or surgical removal of a portion or all of an intervertebral disc. Often, this is followed by implantation of a device between adjacent vertebrae to maintain or restore disc space height. Typically, implantation of such a device is also intended to promote bony fusion between the adjacent vertebral bodies.
One limitation on the size of a device inserted into the disc space is the size of the opening through surrounding tissue that is available to gain access to the disc space. From a posterior approach to the spine, the dura and nerve roots must be mobilized to gain access to the disc space. Similarly, from an anterior approach, the aorta and vena cava must be mobilized to gain access to the disc space. Such mobilization is often limited by the anatomical structures, thus resulting in a relatively small access site. Removal of additional bone to enlarge an entrance to the disc space may weaken the joint between two adjacent vertebra. Moreover, excessive retraction of vessels and neural structures to create a large access opening may damage these tissues. Thus, prior procedures have been limited to placing a first device passable through the available opening on one side of the spine and mobilizing the tissue or vessels to place another similar implant on the opposite side of the spine. Each implant being limited in size by the available access site.
Thus, there remains a need for implantable devices that have a reduced size insertion form and are expandable in the disc space to a larger size for enhancing spine stability and facilitating immobilization via bony fusion.
The present invention contemplates an intervertebral spacer device that has a reduced size configuration for insertion into a disc space and an expanded size configuration to maintain the spacing of the disc space. In one aspect of the present invention, the device includes a pair of arms each having a first end and a second end, the arms being movably coupled at their first ends. When the arms are positioned adjacent one another, the device is in a reduced size configuration for insertion into the disc annulus. The device is laterally expandable in the disc space to an expanded configuration by moving the pair of arms about the first ends in order to increase the dimension of the device perpendicular to the longitudinal axis of the spine while maintaining the inter-space distraction. Preferably, the expanded device creates a cavity that may be filled with bone or bone substitute material for purposes of promoting fusion between the adjacent vertebrae. Preferably, the height of the device in the reduced size configuration is substantially the same as the height in the expanded configuration, with the expanded configuration providing an increased base of support.
In another embodiment of the present invention, the first and second arms each have laterally extending portions extending therefrom that cooperate to engage the first and second arms to one another. Preferably, each of the laterally extending portions defines a plurality of serrations, wherein the serrations of one laterally extending portion of the first arm cooperate in interdigiting fashion with serrations of the corresponding laterally extending portion of the second arm. In one preferred embodiment, the laterally extending portions are provided at the first and second ends of each of the arms. In another preferred embodiment, the pair of arms are pivotably coupled at their first ends, and laterally extending portions are provided at the second ends.
In still a further embodiment, the pair of arms are flexibly attached such that they are compressible into a first smaller configuration and laterally self-expand to a second larger configuration. In one such embodiment, the arms are interconnected by a flexible hinge portion at one end of each arm. In another embodiment, each arm is flexibly connected to a first end portion and an opposing second end portion to form a substantially rectangular shape having flexible side walls. Preferably, the side walls are biased to assume the second larger configuration.
One object of the present invention is to provide a vertebral spacer device that is capable of insertion in a smaller form and laterally expandable within the disc space to an enlarged configuration for supporting the spine.
Other objects and advantages of the present invention will be readily discerned upon consideration of the following written description and accompanying figures.